1. Field of the Invention
The present invention relates to a brake operating device which operates a brake device for braking a vehicle.
2. Description of the Related Art
Generally, a brake operating device which operates a brake device of a vehicle includes a brake pedal and a push rod (output member) connecting the brake pedal with a brake booster device. In the brake operating device, when a driver depresses the brake pedal, the swinging of the brake pedal is transmitted to the brake booster device via the push rod so as to operate the brake device.
Among such brake operating devices, a brake operating device provided with a so-called pedal ratio changing device which can vary the pedal ratio of the brake pedal has been proposed (e.g., Japanese Patent Application Laid-Open No. 5-301565).
In the brake operating device disclosed in the aforementioned laid-open application, the pedal ratio changing device is provided between the brake pedal and the push rod. The pedal ratio changing device is structured by a link, which is supported at the brake pedal and connected to the push rod by a guide pin, an elongated hole, which is formed in the brake pedal and into which a guide pin is inserted, and a return spring which is connected to the guide pin. In this way, the pedal ratio is changed at the time of normal braking operation and at the time of sudden braking operation, so that optimal braking operation can be implemented.
However, in the conventional brake operating device provided with the above-described pedal ratio changing device, the pedal ratio is changed by changing the position of the guide pin inserted into the elongated hole, in accordance with the swinging (depression) angle of the brake pedal or the depression force. The position of the guide pin is determined by the proportion of force by the brake pedal, the push rod and the return spring. However, frictional force is generated at the brake pedal, the push rod, and the return spring and at other parts as well, and the effect of this frictional force is great. As a result, a drawback arises in that it is difficult to reliably obtain a desired, stable pedal ratio, and it is easy for the input/output characteristic determined by the pedal ratio to become unstable.